I see question marks, but I'm not sure if there's a question in there. You seem to have a good grasp of the concept.

if a want to print using iso-8859-1 it could be possible downgrading

You'd get the right result, at the cost of confusing your readers. You'd be saying you're doing one thing (changing the internal format) while actually doing another (changing the encoding of the string).

I see that it's not representing in the iso-8859-1 charset

Correct, iso-8859-1 cannot encode U+201C. cp1252 can. cp1252 is Microsoft's extension of iso-8859-1. It's a commonly used encoding in the Windows world, which is why U+201C is encountered frequently.

we can check if it's downgradable or not using utf8::downgrade($str, 1)

Indeed. I have used that very code to make sure a sub was only given bytes before calling a function that expects to only get bytes. At the same time, it makes sure the bytes aren't internally encoded as UTF-8. Most XS functions can't handle that (which is really a bug in the XS function).

using Encode::encode the unmapped character is printed as an ? question symbol and not report any notice

You'd get the right result, at the cost of confusing your readers. You'd be saying you're doing one thing (changing the internal format) while actually doing another (changing the encoding of the string).

Yes, my example is for understand the basic step of how perl works internally and what I can obtain handle it, in the mayor part it is a theory test, because it must be handle usually with functions like Encode::encode

Indeed. I have used that very code to make sure a sub was only given bytes before calling a function that expects to only get bytes. At the same time, it makes sure the bytes aren't internally encoded as UTF-8. Most XS functions can't handle that (which is really a bug in the XS function).

That's really important, i'll take mental note, of common error using XS functions.

You're very helpful to undestand this topic, it's small but clear thank you again

Ada Lovelace for the palindrome
Albert Einstein for having smelly feet
Alfred Nobel for his contribution to battlefield science
Burkhard Heim for providing the missing link between science and mysticism
Claude Shannnon for riding a unicycle at night at MIT
Donald Knuth for being such a great organist
Edward Teller for being the template for Dr. Strangelove
Edwin Hubble for pretending to be a pipe-smoking English gentleman
Erwin Schrödinger for cruelty to cats
Hedy Lamarr for weaponizing pianos
Hugh Everett for immortality, especially for cats
Isaac Newton for his occult studies
Kikunae Ikeda for discovering the secrets of soy sauce
Larry Wall for his website
Louis Camille Maillard for discovering why steaks taste good
Marie Curie for the shiny stuff
Nikola Tesla for the cool cars
Paul Dirac for speaking one word per hour when socializing
Richard Feynman for his bongo skills
Robert Oppenheimer for his in-depth knowledge of the Bhagavad Gita
Rusi P Taleyarkhan for Cold Fusion
Sigmund Freud for his Ménage ā trois
Theodor W Adorno for his contribution to the reception of jazz
Wilhelm Röntgen for the foundations of body scanners
Yulii Borisovich Khariton for the Tsar Bomba
Other (please explain why)